SA.22c Rubidium Oscillator
Designer Reference and User Guide Revision D
11
3.6
Susceptibility to Input Noise
For applications where the output spectrum phase noise and spur integrity are crucial, the SA.22c must
have a comparatively clean source of DC power (free of spurious current or voltage noise). Connecting
fans, heaters, and other switching devices to the DC supply powering the SA.22c results in degraded
phase noise and spur performance. Best performance is achieved with only one output turned on and
the other frequency outputs turned off.
The Rb atomic frequency source uses a modulation/demodulation scheme with a modulation frequency
of approximately 156 Hz. Inherent in this approach is sensitivity to noise at multiples of the modulation
frequency. This noise is coupled through both the heater and electronic power lines to cause
modulation spurs on the output frequency.
Note: Avoid the modulation frequency and its lower harmonics (roughly up to the tenth harmonic).
3.7
Reliability and Maintenance
The following sections address reliability and maintenance of the SA.22c.
3.7.1
Reliability
The SA.22c is designed with a life of ten years of operation without retuning. To accomplish this, the
major mechanisms impacting the need for maintenance were addressed. Thus, each SA.22c is designed
to have excess rubidium filled in the lamp to last for the required period, sufficient pulling range for the
voltage controlled crystal oscillator, and sufficient dynamic range of the rubidium control loop.
3.7.2
Maintenance
The SA.22c is serviced in the factory only. There is no user service adjustment or maintenance required.
A monitor signal is provided to help the user to track indications of pending end-of-life for the unit with
sufficient notice to avoid a total and sudden failure of the unit. The key indicator of health is the service
indicator that indicates when the rubidium physics package or the on-board quartz oscillator are near to
their operating or control limits.
If the lock signal does not indicate a rubidium lock within the specified time, or the service signal
indicates that the unit has reached the end of its effective life, remove the unit and return it to
Microsemi for service. The service indicator is valid only when the lock signal indicates that the unit is
locked.
For information about how to return a unit for service, see
.
Repairs and Support (see page 14)
